Alloy articles for use at high temperatures



Patented July 4, 1950 ALLOY ARTICLES FOR USE AT HIGH TEMPERATURES Russell Franks and William O. Binder, Niagara Falls, N. Y.,.assignors, by mesne assignments, 1 to-Union Carbide and Carbon Corporation, a

corporation of New York No Drawing. Application May 9, 1946, Serial No. 668,334

3 Claims.

This invention relates to ferrous alloy articles for use at high temperatures, referring more particularly to alloyarticles suitable. forv use in applications Where great strength at high temperatures is required. Y

The trend of modern engineering is toward the utilization of high temperatures for many and diverse operations. For example, chemical processes are today conducted at very high temperatures, a notable instance being petroleum refining. Also, the quest for improved power sources has led to the investigation and development of such devices as superchargers, gas turbines, jet pro pulsion apparatus and the like all operating at high temperatures. These developmentsdemand of the. metallurgist metals and alloys which will Withstand prolonged exposure to temperatures Well above about 700 F. and in many instances well above about 1200 F. The problem is cornplicated by the fact that severe mechanical stress. is often encountered at these temperatures.

For parts of such devices as superchargers, gas turbines, jet propulsion apparatus and thelike, it is necessary to employ alloys that are capable of withstanding severe mechanical stress at high temperatures. Depending upon the design and the intended use of such devices, the temperature ranges at which they operate may be separated into a range between 900 F. and about 1200 F. and into a range upwards of 1200 R, up to about 1500 F. Associated parts and apparatus may be required to withstand temperatures of about 700 F. and above. In devices operating within the lower temperature range, generally much higher stresses are applied than in devices operating above 1200 F. In many instances it is desired that alloys for use in such apparatus be capable of being hot-worked and machined, while in other instances the alloys may be employed in the form of castings. In any event, the alloys must have high strength.

A number of alloys have been proposed for use at high temperatures, but the utility of these alloys has been limited either because they are not hot-workable or machinable, or because they become brittle upon prolonged exposure to high temperatures. One of the characteristics of highly alloyed ferrous materials is that as the iron-base solid solution alloy contains more and more of the alloying metals to increase high temperature strength, the stability of the materials at highv temperatures tends to decrease so that on prolonged exposure to high temperatures the materials become excessively brittle.

. It; is the. principal object of this. invention .tov

provide ferrous alloys suitable for use in applications where temperatures above about 700 F. are normally encountered. A further object is the provision of hot-workable and machinable alloys for use at such elevated temperatures. Another object is the provision of alloys capable of withstanding severe mechanical stress at elevated temperatures above about 700 F. A more specific object is the provision of alloys and articles wrought or cast therefrom capable of withstanding severe mechanical stress at elevated temperatures above about 700 F. up to about 1500 F.

The invention by means of which these objects are achieved is based on the discovery'that the addition of small, properly-proportioned quantities of tungsten, and at least one element selected from the group consisting of boron and aluminum to iron-chromium-cobalt alloys produces a remarkable increase in the high temperature strength of such alloys without detrimentally affecting their high temperature stability.

The invention comprises alloys containing 10% to 30% chromium, 10% to 45% cobalt, 0.5% to.

15% tungsten, and 0.01% to 3% in the aggregate of at least one element selected from the group consisting of boron and aluminum, the maximum boron content being 1.5% and preferably 0.7%

and the minimum aluminum content in the absence of boron being 0.5%, the remainder of the alloys being iron except for incidental impurities and small quantities of elements customarily present in steels of good quality. Up to about 7.5% molybdenum may be present in the alloys particularly if the tungsten is low. Generally preferred ranges for molybdenum and tungsten are 0.5% to 5% molybdenum and 7.5% to 15% tungsten. In the absence of molybdenum the, tungsten content should be at least 7.5%.

Carbon is always present in the alloys of the invention. Preferably it does not exceed about 1%, and if hot working of the alloys is desired, the maximum carbon content should be 0.35%. The boron content is in some measure dependent on the carbon content, a low carbon content permitting the use of a high boron content. Nitrogen is importantly beneficial and is preferably present in a proportion up to 0.25%. Silicon and manganese may be present, the silicon content preferably not exceeding 1% and the manganese content not exceeding 2% if hot working is desired.

A useful test for determining the suitability of materials for use at high temperatures is the so called stress-rupture test. In this test several samples of an alloy to be tested are maintained '3 at a given temperature, each sample being subjected to a difierent measured stress. The time required to cause failure of the samples under these conditions of temperature and stress is determined, and the time and stress values obweldability, particularly the latter property. A1- loys within the composition limits defined may be welded readily by any of the common welding methods, for example, electric arc, oxyacetylene, submerged-melt electric welding, or solid the ability of the alloys of the invention to withstand large stresses at elevated temperatures for prolonged periods of time without failure.

In manufacturing the alloys of this invention care should be taken that the composition limits set forth be closely adhered to with regard to the intended use of the alloys since material variations in the proportions of the several ingredients detrimentally afiect the desired properties. For example, if the alloys are to be employed as castings, the carbon content may be as high as 1%; but if hot-workability is desired, the carbon content should be kept at a maximum ofv about 0.35% and preferably should not exceed 1 70v Similarly, the proportions of molybdenum,

tungsten, aluminum, and boron present in the alloys affect hot-workability and weldabilitv:

Too high a proportion of. any of these elements has. a. detrimental. eiiect .on hot-workability-and.

tained are plotted to yield a curve for the parphase pressure welding, sound, strong and tough ticular material under test. From this curve can welds being produced without undue embrittlebe determined the stress the material will withment of weld metal or base metal, and such welds stand for a given period of time, say 1000 hours, retain their toughness at elevated temperatures. at the particular temperature for which the curve However, if too high a proportion of any of these was drawn. This test provides a convenient elements is present in the alloys, welds produced method of determining the load carrying ability usually suffer fromloss of toughess at elevated of a material. It also gives some indication-of temperatures. whether or not the material becomes embrittled Likewise the proportion of cobalt is important, upon prolonged exposureat the temperature of and should be sufiicient to produce a stable austhe test. A brittle material will break without tenitic alloy. elongation, whereas ductile material will elongate The presence of nitrogen in the alloys of the before failure. invention within the range indicated is important, Stress-rupture tests conducted in the manner nitrogen having a beneficial effect on the high just described indicate that the alloys of the intemperature stability of the alloys. vention maintain great strength at temperatures Being hot-workable, machinable, weldable, and s high a 1 F- d a ve a Such hi castable, and possessing remarkable strength at temperature the alloys possess good ductility. elevated temperatures up to about 1500 F., the Typical examples of the high temperature alloys of the invention are particularly well suited strength of chromium-cobalt steels imparted by to use in the fabrication of articles such as parts the addition of molybdenum, tungsten, and boron of superchargers, gas turbines, jet propulsion apor aluminum in various combinations are indiparatus and the like which are required to with-. cated by the data in the table below. In this stand severe mechanical stress at elevated temtable are reported the results of stress-rupture peratures, Th ir freedom from mbrittl em; tests in which stresses of 25,000 to 40,000 pounds upon prolonged exposure at high temperatures P Square inch W pp o Cast Samples of recommends their use where dependability of the steels to be tested while the samples were operation is essential. maintained at a temperature of 1500 F. The We laim; time in hours required for the sample to fall 1. An alloy article for service at elevated temunder these extremely severe conditions is reperatures upwards of 700 F, and having great ported in the table. I strength and stability when subjected to severe Table Composition-Remainder Substantially All Fe 2%; gg s g gg ff gj Per Per Per Per Per Per Per 25,000 35,000 40,000 5 3 g 3 3 a 3 g p. s. 1. p. s.1. 5.5.1.

18.5 35 4 4 0.51 1 0.08 104 20.0 35 2 10 0.51 N11 0.11 1, 483 787 18.5 35 s 10 0.55 Nil 0.01 2125 18.5 55 N11 10 0.01 Nil 0. 09 1,992 550 1s N11 15 0.55 Nil 0.01 400 14s 18 40 Nil 15 0.52 Nil 0.84- 285 18 10 N11 15 0.63 N11 0.12 285 18 40 Nil 15 0. 02 Nil 0.01 2,184 309 159 is 40 N11 15 1.3 Nil 0.05 2,150 235 1 N 0 Test. 1 No Failure. 8 Tested 30,000 p. s. i. stress.

The data in the above table clearly illustrate 55. stresses for pr lo P d at Such elevated to cobalt; 0% to 7.5% molybdenum; 0.5% to 15 tungsten, the tungsten content being at least 7.5% in the absence of molybdenum; 0.01% to 3% in the aggregate of at least one element selected from the group consisting of boron and aluminum, the maximum boron content being 0.7% and the minimum aluminum contentinthe absence of boron being 0.5%; carbon in an amount not exceeding 0.35%; nitrogen in an amount not exceeding 0.25%; the remainder be ing iron and incidental impurities.

2. An alloy article for service at elevated te peratures upwards of 700 F. and having great.

strength and stability when subjected to severe stresses for prolonged periods of time at such. elevated temperatures, said article being composed of a machinable, weldable, castableand hot-workable alloy consisting of 10% to 30% chromium; 10% to 45% cobalt; 0% to 5% molybdenum; 7.5% to 15% tungsten, the tungsten content being at least 7.5% in the absence of molybdenum; 0.01% to 3% in the aggregate of at least one element selected from the group consisting of boron and aluminum, the boron content being no more than 0.7% and the minimum aluminum content in the absence of boron being 0.5%; carbon in an amount no more than 0.2% nitrogen in an amount no more than 0.25%; the remainder being iron and incidental impurities.

3. A ferrous alloy article for service at elevated temperatures and having great strength and, stability when subjected to stresses upwards of 25,000 p. s. i. for prolonged periods of time at 1500 F., said article being composed of a machinable, weldable, castable and hot-workable alloy consisting substantially of 18% chromium; 40% cobalt; 15% tungsten; 0.6% boron; 0.12% carbon; the remainder iron and incidental impurities.

RUSSELL FRANKS. WILLIAM G. BINDER.

REFERENCES CITED The following references are of record in the file of this patent:

6 UNITED STATES PATENTS Number Name Date 1,376,062 Albrecht Apr. 26, 1921 1,729,154 Clawson Sept. 24, 1929 1,774,862 Wissler Sept. 2, 1930 2,213,207 De Golyer Sept. 3, 1940 2,244,517 De Golyer June 3, 1941 2,245,366 Rohn June 10, 1941 2,309,372 Wissler Jan. 26, 1943 2,397,034 Mohling Mar. 19, 1946 2,398,702 Fleischmann Apr. 16, 1946 2,432,614 Franks et a1 Dec. 16, 1947 2,432,615 Franks et a1 Dec. 16, 1947 2,432,618 Franks et al Dec. 16, 1947 FOREIGN PATENTS Number Country Date 219,293 7 Great Britain May 7, 1925 308,549 Great Britain Mar. 28, 1929 OTHER REFERENCES Kinzel and Franks: Alloys of Iron and Chromium, published by McGraW-Hill Book Co. N. Y., vol. II, 140, pages 87, 88, 180, 192, 194, 455.

Progress Report on NDRC, Research Project NRC-8, P. B. 39, 578, October 7, 1942, pages 1-21 inclusive (particularly page 5. Declassified to open February 28, 1946. 

1. AN ALLOY ARTICLE FOR SERVICE AT ELEVATED TEMPERATURES UPWARDS OF 700*F. AND HAVING GREAT STRENGTH AND STABILITY WHEN SUBJECTED TO SXEVERE STRESSES FOR PROLONGED PERIODS AT SUCH ELEVATED TEMPERATURES, SAID ARTICLE BEING COMPOSED OF A MACHINABLE, WELDABLE, CASTABLE AND HOT-WORKABLE ALLOY CONSISTING OF 10% TO 30% CHROMIUM; 10% TO 45% COBALT; 0% TO 7.5% MOLYBDENUM; 0.5% TO 15% TUNGSTEN, THE TUNGSTEN CONTENT BEING AT LEAST 7.5% IN THE ABSENCE OF MOLYBDENUM; 0.01% TO 3% IN THE AGGREGATE OF AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF BORON AND ALUMINUM, THE MAXIMUM BORON CONTENT BEING 0.7% AND THE MINIMUM ALUMINUM CONTENT IN THE ABSENCE OF BORON BEING 0.5%; CARBON IN AN AMOUNT NOT EXCEEDING 0.35%; NTIROGEN IN AN AMOUNT NOT EXCEEDING 0.25%; THE REMAINDER BEING IRON AND INCIDENTAL IMPURITIES. 